The present invention relates to an electron-beam apparatus and image forming apparatus and, more particularly, to an electron-beam apparatus and image display apparatus for accelerating, at an accelerating potential, electrons emitted by an electron-emitting device.
Conventionally, two types of devices, namely thermionic and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction emission type electron-emitting devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
A known example of the surface-conduction emission type electron-emitting devices is described in, e.g., M. I. Elinson, xe2x80x9cRadio E-ng. Electron Phys., 10, 1290 (1965) and other examples will be described later. The surface-conduction emission type electron-emitting device utilizes the phenomenon that electrons are emitted by a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction emission type electron-emitting device includes electron-emitting devices using an Au thin film [G. Dittmer, xe2x80x9cThin Solid Filmsxe2x80x9d, 9,317 (1972)], an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)], a carbon thin film [Hisashi Araki et al., xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 17 is a plan view showing the surface-conduction emission type electron-emitting device by M. Hartwell et al. Referring to FIG. 17, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 17. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 17 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience.; However, this does not exactly show the actual position and shape of the electron-emitting portion. In the above surface-conduction emission type electron-emitting devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In forming processing, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after forming processing, electrons are emitted near the fissure.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenium conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
FIG. 18 is a sectional view showing the FE type device by C. A. Spindt et al. In FIG. 18, reference numeral 3010 denotes a substrate; 3011, an emitter wiring made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, a gate electrode. In this device, a voltage is applied between the emitter cone 3012 and gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012. As another FE type device structure, there is an example in which an emitter and gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of FIG. 17.
A known example of the MIM type electron-emitting devices is described in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961).
FIG. 19 is a sectional view showing a typical example of the MIM type device structure. In FIG. 19, reference numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 100 xc3x85; and 3023, an upper electrode made of a metal and having a thickness of about 80 to 300 xc3x85. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper and lower electrodes 3023 and 3021 to emit electrons from the surface of the upper electrode 3023.
Since the above-described cold cathode devices can emit electrons at a temperature lower than that for thermionic cathode devices, they do not require any heater. The cold cathode device has a structure simpler than that of the thermionic cathode device and can shrink in feature size. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the thermionic cathode device is low because thermionic cathode device operates upon heating by a heater. For this reason, applications of the cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the surface-conduction emission type electron-emitting devices have a simple structure and can be easily manufactured, and thus many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the assignee of the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of the surface-conduction emission type electron-emitting devices to, e.g., image forming apparatuses such as an image display apparatus and image recording apparatus, charge beam sources, and the like have been studied. Particularly as an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the assignee of the present applicant, an image display apparatus using a combination of a surface-conduction emission type electron-emitting device and a fluorescent substance which emits light upon irradiation of an electron beam has been studied. This type of image display apparatus using a combination of the surface-conduction emission type electron-emitting device and fluorescent substance is expected to exhibit more excellent characteristics than other conventional image display apparatuses. For example, compared with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require any backlight because it is of a self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the assignee of the present applicant. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat panel display reported by R. Meyer et al. [R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)].
An application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the assignee of the present applicant.
Several types of cold cathode electron sources have been described above. There is known another structure using an anode electrode for attracting an electron beam from the electron source of a cold cathode device.
Further, there is known a method of supplying, from a switching type high-voltage power source, an accelerating potential for accelerating electrons from an electron source. For example, a CRT uses a flyback type switching power source. An output potential from the switching type high-voltage power source includes an AC component (to be also referred to as a ripple hereinafter). To reduce this ripple, a smoothing circuit may be used, which increases the cost and size. Particularly, a general high-voltage power source uses a high-cost, large-volume capacitor, and the use of a satisfactory smoothing circuit increases the cost and size. Even with the use of the smoothing circuit, a ripple must be permitted to a certain degree in order to reduce the cost or suppress an increase in size.
It is an object of the present invention to realize a preferable image display apparatus and, more particularly, a preferable structure in a case in which an accelerating potential for accelerating electrons from an electron-emitting device includes an AC component.
One aspect of the present invention comprises the following arrangement.
An electron-beam apparatus comprises
an electron source having a plurality of sets each including a plurality of electron-emitting devices, each set being periodically selected, and the plurality of electron-emitting devices in each set being selected and allowed to simultaneously emit electrons,
an accelerating electrode for receiving a potential for accelerating electrons emitted by the electron-emitting device, and
a power source having an output potential including an AC component, a frequency of the AC component being controlled to be equal to a selection frequency for each set in the electron source, and the output potential being supplied to the accelerating electrode.
In this specification, xe2x80x9cthe output potential includes an AC componentxe2x80x9d means that the value periodically varies.
Another aspect of the present invention comprises the following arrangement.
An electron-beam apparatus comprises
an electron source having a plurality of sets each including a plurality of electron-emitting devices, each set being periodically selected, and the plurality of electron-emitting devices in each set being selected and allowed to simultaneously emit electrons,
an accelerating electrode for receiving a potential for accelerating electrons emitted by the electron-emitting device, and
a power source having an output potential including an AC component, a frequency of the AC component being controlled to be equal to a multiple of an integer of not less than 2 of a selection frequency for each set in the electron source, and the output potential being supplied to the accelerating electrode.
Still another aspect of the present invention comprises the following arrangement.
An electron-beam apparatus comprises
an electron source having a plurality of sets each including a plurality of electron-emitting devices, each set being periodically selected at a frequency f2, and the plurality of electron-emitting devices in each set being selected and allowed to simultaneously emit electrons,
an accelerating electrode for receiving a potential for accelerating electrons emitted by the electron-emitting device, and
a power source having an output potential including an AC component, letting q be at least any natural number of 1 to 10, a frequency f1 of the AC component being controlled to satisfy equation (1), and the output potential being supplied to the accelerating electrode,
f1=n/(q*T)xe2x80x83xe2x80x83(1)
where n is an arbitrary natural number, and T is a period from time at which any one of the electron-emitting devices is selected and allowed to emit electrons to time at which the electron-emitting devices is selected again and allowed to emit electrons.
In this case, the frequency f1 satisfies equation (1) preferably when q is any natural number of 1 to 5, more preferably when q is any natural number of 1 to 3, and still more preferably when q is 1. The frequency f1 preferably satisfies equation (1) when it satisfies inequality (2):
f1 less than f2xe2x80x83xe2x80x83(2)
In each aspect, it is desirable that the apparatus further comprise, in correspondence with each set, a common wiring commonly connected to the plurality of electron-emitting devices in each set, and the set be selected by applying a selection potential different from potentials of other common wirings to the common wiring of the set to be selected. In this arrangement, the electron-beam apparatus preferably further comprises, in correspondence with the plurality of electron-emitting devices in each set, a plurality of wirings for applying a potential for emitting electrons from the electron-emitting device in cooperation with the selection potential applied to the common wiring. These wirings may be shared by electron-emitting devices belonging to separate sets. This arrangement includes one known as matrix wiring. The selection potential applied to the common wiring is desirably set such that each device is not substantially driven before a potential applied to a plurality of wirings laid out in correspondence with a plurality of devices in each set reaches a value which satisfies a predetermined condition, and the device is driven when the potential applied to a plurality of wirings laid out in correspondence with a plurality of devices in each set reaches the value which satisfies the predetermined condition. Emission of electrons from the electron-emitting device is desirably controlled by controlling a potential value or an application time of a potential applied to the plurality of wirings for applying the potential for emitting electrons from the electron-emitting device in cooperation with the selection potential applied to the common wiring. The potential or a flowing current may be controlled.
Each aspect can be preferably adopted when the electron-emitting device is a cold cathode device, and can be more preferably adopted when the electron-emitting device is a surface-conduction emission type electron-emitting device.
In each aspect, the power source can preferably use a switching power source which may be a forward type switching power source, flyback type switching power source, or resonance type switching power source.
In each aspect, the set is selected based on an input horizontal sync signal, and the power source is driven based on the horizontal sync signal to generate the output potential. The power source is driven based on the horizontal sync signal at the same frequency as the frequency of the horizontal sync signal, or a frequency which is controlled based on the frequency of the horizontal sync signal and is different from the frequency of the horizontal sync signal. The frequency for driving the power source can be controlled by a phase-locked loop. The horizontal sync signal can be used as a target to be compared by the phase-locked loop.
An image forming apparatus according to the present invention comprises a fluorescent substance for emitting light upon reception of electrons emitted by the electron-emitting device in the above-described electron-beam apparatus. In this case, the power source is desirably driven based on a sync signal included in an input image signal to generate the output potential. A selection frequency for the set is preferably based on the sync signal included in the image signal.
Still another aspect of the present invention comprises the following step.
A method of driving an electron-beam apparatus having
an electron source having a plurality of sets each including a plurality of electron-emitting devices, each set being periodically selected, and the plurality of electron-emitting devices in each set being selected and allowed to simultaneously emit electrons,
an accelerating electrode for receiving a potential for accelerating electrons emitted by the electron-emitting device, and
a power source for supplying an output potential including an AC component to the accelerating electrode, comprises the step of
controlling a frequency of the AC component of the output potential to be equal to a selection frequency for each set in the electron source.
Still another aspect of the present invention comprises the following step.
A method of driving an electron-beam apparatus having
an electron source having a plurality of sets each including a plurality of electron-emitting devices, each set being periodically selected, and the plurality of electron-emitting devices in each set being selected and allowed to simultaneously emit electrons,
an accelerating electrode for receiving a potential for accelerating electrons emitted by the electron-emitting device, and
a power source for supplying an output potential including an AC component to the accelerating electrode, comprises the step of
controlling a frequency of the AC component of the output potential to be equal to a multiple of an integer of not less than 2 of a selection frequency for each set in the electron source.
Still another aspect of the present invention comprises the following step.
A method of driving an electron-beam apparatus having
an electron source having a plurality of sets each including a plurality of electron-emitting devices, each set being periodically selected at a frequency f2, and the plurality of electron-emitting devices in each set being selected and allowed to simultaneously emit electrons,
an accelerating electrode for receiving a potential for accelerating electrons emitted by the electron-emitting device, and
a power source for supplying an output potential including an AC component to the accelerating electrode, comprises the step of
letting q be at least any natural number of 1 to 10, controlling a frequency f1 of the AC component of the output potential to satisfy equation (1),
f1=n/(q*T)xe2x80x83xe2x80x83(1)
where n is an arbitrary natural number, and T is a period from time at which any one of the electron-emitting devices is selected and allowed to emit electrons to time at which the electron-emitting devices is selected again and allowed to emit electrons.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.